The invention relates to an adhesion-promoting additive for an ink for imprinting glass comprising at least one silane, an ink comprising at least one solvent, an adhesion-promoting agent and a pigment, a method for printing a surface of glass with an inkjet printer, wherein ink is applied in the form of droplets onto the surface of the glass, as well as the use of the additive.
The decoration or marking (“labelling”) of glass and glass products is important in many areas of business. There is an enormous demand in the field of architecture for individually designed glass both for internal and external use, in the automotive field, in advertising, in the field of decorating household objects etc. Whilst large amounts of identically printed glasses and glass products are usually produced by screen-printing methods, inkjet printer applications for printing individually designed glass in small batches or with frequently changing motifs are an interesting alternative.
For decorative inkjet printing on different substrates, such as e.g. plastics, paper, etc., there are a number of pigmented organic ink formulations, which can be cured thermally or by UV radiation. Despite the amount of inks available said formulations have considerable disadvantages with regard to their adhesion onto glass, their scratch-resistance and resistance to water or solvents.
Alternative approaches involve burning in inorganically pigmented inks. Said formulations, which in addition to pigments and other typical ink components also often contain fritted glass (e.g. bismuth oxide, lead-containing materials etc.), after the burning process have good resistance to abrasion and the effect of water and solvents, but due to the toxicity of some pigments and fritted glass, the difficulty of grinding pigments and fritted glass, and due to the complicated burning-in process are uneconomical to use and may be unhealthy.
For these reasons for many applications, which have strict requirements with regard to adhesion and scratch resistance, attempts have been made to modify UV or thermally curable organic graphic inks so that the criteria required for glass printing are satisfied. In this case, various different solution strategies have been pursued, including in particular the admixing of organic polymers (e.g. novolac resins, silicon resins) to increase scratch resistance. Likewise attempts have been made to increase the stability of glass printing by applying various primers (e.g. Pyrosil®). Furthermore, the admixing of silanes for the covalent bonding of the printed pattern onto the glass surface is known from the prior art.
Thus e.g. DE 696 030256 T2 describes an ink composition for an inkjet printer which has improved adhesion and abrasion resistance on glass, PET or aluminium in humid conditions. The composition comprises an organic solvent, a flexible thermoplastic polyurethane resin, a colouring means, a silicon resin and a silane. The proportion of silane is between 0.5 wt. % and 2.5 wt. %. Epoxy alkyl oxysilane and amino alkyl alkoxy silane are given as the silanes.
From DE 697 01 873 T2 an inkjet printing ink for marking containers, such as bottles, is known, which during the printing can have a film of condensation on their surface. In order to address this problem an alkoxysilane polyalkylene imine is added as an adhesion accelerator to the printing colour.